Researchers have demonstrated a new optical wiring technique for carrying out sensitive quantum operations on atoms. In this technique, the control laser light is delivered directly inside a chip. This should make it possible to build large-scale quantum computers based on trapped atoms.
Already in current small-scale systems, conventional optics are a significant source of noise and errors—and that gets much harder to manage when trying to scale up. The more qubits one adds, the more complex the optics for the laser beams become which is needed for controlling the qubits. By integrating tiny waveguides into the chips that contain the electrodes for trapping the ions, we can send the light directly to those ions. In this way, vibrations of the cryostat or other parts of the apparatus produce far less disturbance.
The researchers commissioned a commercial foundry to produce chips that contain both gold electrodes for the ion traps and, in a deeper layer, waveguides for laser light. At one end of the chips, optical fibers feed the light into the waveguides, which are only 100 nanometres thick, effectively forming optical wiring within the chips. Each of those waveguides leads to a specific point on the chip, where the light is eventually deflected towards the trapped ions on the surface.